If I make extra-double sure to only copy the command up to the last character, will that stop the newline from being copied?
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mattloaf1Dec 12 '09 at 17:17

It will indeed. Copying and pasting is generally application specific on Windows, as they control access to the clipboard. So it can depend where you are copying from and what that does, but generally if you're quite careful about setting the marker just to the last character, and not further onto the end of the line (it's like an invisible line!) you normally get away with it. If you're not sure, I sometimes find selecting right to left instead of left to right can work
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Philip ReynoldsDec 12 '09 at 17:21

I would guess that you get a linefeed copied into the clipboard sometimes. To check if this is the case, try running clipbrd.exe or simply pasting the contents into your favorite control-char-displaying editor.